Environmental Engineering Reference
In-Depth Information
Another issue that regulatory authorities find very difficult to address is that toxic
substances are tested and measured in isolation from one another. However, my body un-
doubtedly contains a complex cocktail of substances I have acquired from my environment
but have been unable to excrete. Therefore, what we may be interested in knowing is the
combined risk of this cumulative body burden. The toxicity of a substance is often related
to its molecular structure and shape. For example, dioxins, furans and a particular class of
PCBs (known as coplanar PCBs) are sufficiently alike that toxicologists are able to estim-
ate their toxicity in relation to one form of dioxin (2,3,7,8-TCDD). However, no similar
method exists to group substances in chemical risk assessments and we still have little no-
tion of the true impact of the complex mixture of toxic substances that are now present in
our bodies even before we are born.
Itistimetoreturntoourearlierquestionastowhethertheworldhasheard,understood
and acted on the insights given by the Arctic Messenger. I think it has heard, understood
a little, acted a little and misunderstood or ignored almost completely the crucial element.
We cannot continue to complacently regard our environment as a convenient sewer into
which we can dump persistent, biomagnifying toxic substances even if such substances
show very little acute toxicity. The ponderous strategy of applying regulatory controls only
after a huge pollutant inventory has been accumulated in the environment and is exerting
its inevitable toll on wildlife, fish and human health is not only amoral but also unsustain-
able.
The Minamata Convention may escape some of the future problems concerning POPs
because it deals with a single substance. However, we will face an unwanted legacy for
many years because air-ocean modelling indicates that the oceans have not yet reached
equilibrium with current atmospheric levels of mercury, which stays in the upper ocean
above a depth of 200 metres for about 30 years and for centuries in intermediate and deep
waters. This is much longer than the one-year residence time in the lower atmosphere.
Thus, removal from the ocean takes much longer than does removal from the air, so con-
centrations will change more slowly.
Search WWH ::
Custom Search